x1 <- c(1018.4,1258.9,1359.4,1545.6,1761.6,
	  1960.8,2295.5,2541.6,2763.9,3204.3,
	  3831.0,4228.0,5017.0,5288.6,5800.0,
	  6882.1,9457.2,11993.0,13844.2,14211.2,
        14599.6)
x2 <- c(1607.0,1769.7,1996.5,2048.4,2162.3,
        2375.6,2789.0,3448.7,3967.0,4585.8,
        5777.2,6484.0,6858.0,8087.1,10284.5,
	  14143.8,19359.6,24718.3,29082.6,32412.1,33429.8)
x3 <- c(138.2,143.8,195.5,207.1,220.7,
	  270.6,316.7,417.9,525.7,665.8,
	  810.0,794.0,859.4,1015.1,1415.0,
        2284.7,3012.6,3819.6,4530.5,4810.6,
       5262.0)
x4 <- c(96259,97542,98705,100072,101654,
	  103008,104357,105851,107507,109300,
	  111026,112704,114333,115823,117171,
	  118517,119850,121121,122389,123626,
	  124810)
x5 <- c(2239.1,2619.4,2976.1,3309.1,3637.9,
        4020.5,4694.5,5773.0,6542.0,7451.2,
	  9360.1,10556.5,11365.2,13145.9,15952.1,
	  20182.1,26796.0,33635.0,40003.9,43579.4,
	  46405.9)
x6 <- c(50760,39370,44530,39790,33130,
	  34710,31890,44370,47140,42090,
	  50870,46990,38470,55470,51330,
        48830,55040,45821,46989,53429,
	  50145)
y <- c(1132.3,1146.4,1159.9,1175.8,1212.3,
	 1367.0,1642.9,2004.8,2122.0,2199.4,
	 2357.2,2664.9,2937.1,3149.5,3483.4,
	 4349.0,5218.1,6242.2,7408.0,8651.1,
	 9876.0)

model <- lm(y~x1+x2+x3+x4+x5+x6)
step(model,direction='backward')
step(model,direction='both')